Aramids, particularly those that form lyotropic solutions or can be spun as anisotropic melts, have exceptionally good tensile modulus, but sometimes have somewhat low tensile strengths and even lower elongations. The lower elongations and tensile strengths mean these aramids have relatively low toughness. These aramids also often have very good high temperature properties. One goal in aramid technology is to develop aramids which have relatively high moduli, tensile strength and elongation, while maintaining good high temperature properties.
The aramids described herein have such a combination of properties. They are made from repeat units formally derived from 4,4 '-bis (3-aminophenoxy)bi-phenyl, p-phenylenediamine and terephthalic acid.
U.S. Pat. No. 4,217,227 generically describes a variety of aramids in which the portion derived from the diamine has multiple phenyl rings present. Such generic formulas could include 4,4 '-bis (3-aminophenoxy)biphenyl, but this compound is not specifically mentioned. These aramids are said to be useful for semipermeable membranes.
Japanese Patent Application 3-31324 describes an aramid containing repeat units derived from 4,4 '-bis (3-aminophenoxy)biphenyl and terephthalic acid. These aramids have relatively poor high temperature properties, with glass transition temperatures well below 300.degree. C., and melting below about 350.degree. C. No mention is made of the presence of repeat units derived from p-phenylenediamine in this aramid.